HYDROIDA. 587 
IN the family Oculinidze, the corallum is branched and tree-like, and is here 
represented by our only known British form, the TUFI CORAL, It is very 
rare, and but seldom taken in our seas. As may be seen from the illustration, 
the corallum resembles a massive, thickly-branched tree, The maividual 
corals are apout half an inch in height, and the same in diameter. 
WE now arrive at the Hydroida, which are known by the internal cavity 
being simple and the creature increasing by buds thrown out from the sides. 
IN the Sertulariadze the buds are inclosed in vesicles, and do not break 
away when adult. They are in cup-like cells, which lave no fvuotsta:ks, 
The reproduction of these beings is very curious, for it is known that they 
Seritlaria filicula. Serlutas ta vOse@. 
Sertularia filicula (magnified. ) 
can be propagated by cuttings just like plants, as well as by cell vesicles, and 
that in the latter case the first stage of the young closely res:mbles that of 
the young Medusa already mentioned. They also reproduce by offshoots ; 
and it is very likely that their capabilities in this respect are not limited 
even to these three methods. 
Any of the common Sertularize affords a good example of this family ; and 
_ as they are easily pr cured, they are verv valuable a:ds to those who wish to 
study the structure of these beautiful beings. Even the empty polypidon is 
not without its clegance, and is often mad- up into those flattened bouquets 
of so called sea-weeds, which are sold in such quantities at sea-side bathing 
towns. But when the whole being is full of life and health. its mult tndinous 
cells filed with the delicate polypes, each furnished with more than twenty 
tentacles all moving in the water, its beauty defies description. These little 
polypes are wonderfully active and suspicious. At the least alarm, they 
retreat into their cells as if withdrawn by springs, and when they again push 
out their tentacles, it is in a very wary and careful manner, 
